Directed Assembly of Metal-Cyanide Cluster Magnets

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

This award to the University of California at Berkeley supports the work of Professor Jeffrey R. Long, Department of Chemistry, aimed at the synthesis of high-nuclearity transition-metal cyanide clusters that can function as single-molecule magnets. The project is supported by the Inorganic, Bioinorganic, and Organometallic Chemistry program in the Chemistry Division and by the Solid State Chemistry program in the Division of Materials Science. A series of cubic clusters with varying metal constituents will be prepared. The cluster geometry is based on a single cage excised from a Prussian Blue type structure and consists of a cube of metal atoms with each edge spanned by a linear cyanide bridge and each corner capped by a tridentate tacn (1,4,7-triazacyclononane) ligand. Two variants of the cluster are presently known, one with eight cobalt atoms, and one with four chromium and four cobalt atoms. Paramagnetic metal centers will be used to prepare additional members of the series, giving rise to a series of compounds with total ground state spin states ranging from S=0 to S=10, in even integral values. Larger clusters will also be synthesized in order to achieve higher total spin states. This can be accomplished by removing the capping ligand from one of the reactant molecules to promote cluster growth. A related series of compounds with an edge-bridged cubic structure will be prepared; total spin values as high as S=26 are expected. Some less symmetric prolate double-cube clusters will also be pursued, as well as a ferromagnetically coupled pentagonal bipyramidal cluster with an S=18 ground state. The clusters synthesized in this research will exhibit axial magnetic anisotropy as well as overall magnetic anisotropy. Magnetic behavior will be examined using variable temperature susceptibility measurements and, when warranted, physical parameters relevant to data storage. Cluster magnets have potential applications in high-density data storage and for investigation of phenomena such as quantum tunneling of magnetization. These compounds have somewhat simpler structures and magnetic exchange pathways than some systems that have been studied previously, and so it is anticipated that determining important design features will be more straightforward. Students involved in this project will learn advanced synthesis methods and have an interdisciplinary experience in chemistry, materials, and physics relevant to nanoscience and engineering.